Drawing+Lewis+Structures

__**Drawing Lewis Structures**__

1. **Draw a skeleton structure**. A skeleton structure is a rough map showing the arrangement of atoms within the molecule. In general, you need to determine the skeleton structure experimentally, but here are a few guidelines for predicting skeleton structures from molecular formulas. > 2. **Count total valence electrons**. > 3. **Connect the structure**.
 * central atoms are usually
 * the largest atoms, or
 * the least electronegative atom
 * H and the halogens are usually outside (terminal) atoms
 * Don't put more than four atoms around a central atom unless the central atom is third period or lower
 * add the number of electrons in the valence shells of all atoms in the molecule
 * if the molecule is charged, add an electron for each negative charge and subtract an electron for each positive charge
 * draw a bond between the central atom and each outside atom
 * each bond uses 2 valence electrons

4. **Place electrons on outside atoms**.
 * complete the octet for each of the terminal atoms in your skeleton structure
 * if you run out of electrons at this point, complete the 2 for 1 rule (erase 2 lone pair, and replace with 1 bond on the central atom to share - this will create a double bond or a triple bond)